Lead-bearing brass, a Cu-Zn-Pb ternary alloy, is widely used for industrial materials because of its free cutting property. The lead content of the alloy is adjusted taking account of cutting properties required. For instance, four kinds of free-cutting brass are defined in Japanese Industrial Standards.
A lead content of 3.0 to 3.5 weight % is said to be most effective to obtain free cutting property. These Cu-Zn-Pb ternary alloys are mainly used for livelihood devices and tools, especially for materials coming into contact with water, such as in devices for water supply. Lead-bearing brass, however, allows lead to dissolve into water in contact with the alloy used in tap devices. Such lead dissolution must be taken into account from the view point of environmental hygiene. Recently, the progress in water source development leads to a greater variety in quality of tap water. Further, hot water is used more widely as the hot water equipments are more and more popular. Therefore, the quality and the temperature of water must be taken into account in connection with lead dissolution.
There are other problems attended with lead-bearing brass. Casting of lead-bearing brass results in, sometimes, gravity segregation owing to the difference in density between lead and brass (the density of lead is 9.81 and that of brass is 7.32 at 1000.degree. C.), as well as uneven distribution and particle size of lead between outer and inner parts of an ingot of a larger size designed for greater efficiency of production, due to the difference in cooling rate within the ingot, causing fluctuation of product quality. Lead-bearing brass also suffers from occasional fracturing in the course of hot forging or other hot forming, while cold working subsequent to a hot process also causes cracks. Such fracture may be attributed to the distribution state of lead deposited in grain boundaries (or sub-grain boundaries) in the solidified alloy because lead does not form a solid solution with either copper or zinc. Free cutting property is also impaired remarkably by a hot process such as hot extrusion and heat annealing due to coagulation of lead particles during the heating.